The invention relates to a method for determining the actually available amount of energy of an energy storage module having a plurality of individual storage elements connected in series.
In the case of known energy storage systems, the actually available amount of energy is determined analogous to the present state of charge while using a high-expenditure sensor system. For battery or accumulator systems, the state of charge (SOC) of the energy storage device can be determined by using current sensors by ampere hour metering. Here, the state of charge (indicated, for example, as a percentage between 0% equaling discharged and 100% equaling fully charged) supplies only inexact information concerning the amount of energy of an energy storage system actually available. In the case of an energy storage device constructed as a capacitor, the state of charge is indicated, for example, in correlation with the output voltage of the capacitor. However, aging or defects may have the result that the accumulator or the capacitor, for example, can no longer be fully discharged, in which case the actual amount of energy that is usable is less than suggested by the state of charge of the energy storage device. As a result of the ampere hour metering known from the state of the art for determining the state of charge of accumulator or battery systems or the like, individual cells of the storage device may be overloaded sporadically during the operation of the system which, in turn, leads to a reduction of the useful life of the storage system.
It is an object of the invention to eliminate the above-described disadvantages and to provide a method of determining the actually available amount of energy in an energy storage device, by which the actually available amount of energy can be determined more precisely. Furthermore, it is an object of the invention to use as few additional components as possible for the conversion and to thereby arrive at a space- and cost-saving solution.
According to the invention, a method is provided for determining the actually available amount of energy in an energy storage module having a plurality of storage cells connected in series. For determining the available amount of energy, voltage limits (limit voltages) are dynamically determined or “learned” and are linked to an also determined storage capacity (actual capacity). According to the invention, it is provided that, in particular, at least one voltage limit (the upper or the lower voltage limit) is dynamically determined and, by way of this voltage limit, in connection with the determined actual storage capacity of the energy storage module, the actually available amount of energy in the energy storage module is determined. The other of the two voltage limits can also be predetermined as an invariable fixed value.
In a particularly preferred embodiment of the invention, a lower limit voltage as well as an upper limit voltage is dynamically determined for the energy storage module—and thereby virtually a dynamic voltage window is determined. In this case, the upper limit voltage will be determined in that, during a charging operation of the energy storage module, as soon as a maximally permissible upper cell voltage (for example, a manufacturer-specific maximally permissive upper voltage) has been reached on at least one storage element, (a first condition signal is generated), the upper limit voltage of the energy storage module is determined by the summation of all cell voltages of all series-connected storage elements of the energy storage module existing at this point-in-time. Analogously, the lower limit voltage is determined in that, during a discharging operation of the energy storage module, as soon as a minimally permissible lower cell voltage (for example, a manufacturer-specific minimally permissible lower voltage) has been reached on at least one storage element, (a second condition signal is generated), the lower limit voltage of the energy module is determined by the summation of all cell voltages of all series-connected storage elements of the energy storage module existing at this point-in-time. The determination of the upper and/or the lower limit voltage takes place dynamically. The predetermined voltage limits of the storage cells are therefore advantageously monitored in a continuous manner. When the predetermined maximally permissible upper cell voltage is reached, the upper limit voltage of the energy storage module will be determined and/or when the minimally permissive lower cell voltage is reached/occurs, the lower limit voltage of the energy storage module is determined or redetermined.
For determining the maximally permissible upper or the minimally permissible lower cell voltage (over- and undervoltage determination for the individual cells), reference is made at this point to European patent document EP 851 556 A1 (having U.S. counterpart U.S. Pat. No. 5,850,136), as well as to international application PCT/EP2006/02291, which is not a prior publication, both of which are incorporated by reference herein. For example, by determining the under- and overvoltage for the individual cells, in the event of the appearance of a flag (indication of a signal condition or event), the respectively existing voltage value of the storage module is stored in this case.
In connection with the determination of the actual storage capacity, reference is made in this regard to German patent document DE 10 2005 025 616 A1, which is also incorporated by reference herein.
Within the meaning of the invention, the actual storage capacity of the energy storage module is the current maximal actual storage capacity of the energy storage module which, as a result of aging or defects or the like, in the course of the operating time (or useful life), as a rule, falls below the original value when new (first start-up). Within the meaning of the invention, the momentarily available amount of energy is the amount of energy which is actually available—thus, the amount of energy which is currently present within the scope of the actually existing voltage limits (lower and upper limit voltage) as well as the actual storage capacity of the energy storage module changed because of the possibly (in comparison to the condition when new (first startup)) changed limit voltages of the energy storage module.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.